1. Field of the Invention
This invention relates to an image forming apparatus such as a copier, a printer, etc., and in particular to an image forming apparatus employing an intermediate transfer belt having a seam, which is capable of suppressing any adverse influence of the seam to obtain a high quality image.
2. Discussion of the Background
In an image forming apparatus such as an optical beam printer a drum type photoconductive member (PC member) is provided to rotate while receiving a scan of a beam having a color component in a main scanning direction in accordance with image data transmitted from either an image reading section or a host computer. Then, latent images are formed with color toner on the PC member and developed to be toner images in accordance with the color component. Subsequently, respective color toner images are transferred and superposed on an intermediate transfer belt one after another, and thereby a full-color image is formed in accordance with the image data.
It has been proposed to utilize a sensor to detect a full-color matching pattern formed on an intermediate transfer belt so that an image formation condition, such as an amount of toner to be supplied or pumped toward a latent image, can be controlled in accordance with data obtained by the sensor, to form a high quality color image in accordance with the image data.
In such a system, an intermediate transfer belt having a ring shape track requires a highly precise peripheral length in a conveyance direction to form a high quality image. Such an intermediate transfer belt is generally formed by connecting leading and trailing ends of a strip-shaped belt in a prescribed peripheral length. Thus, the intermediate transfer belt necessarily includes a seam. As a result, when a usage life exceeds a prescribed level, and accordingly a prescribed time period has elapsed, the intermediate transfer belt needs be replaced with a new one. That is, over time a fixation condition of the seam physically changes, and thereby the peripheral length sometimes deviates beyond an allowable range.
Further, in such a case, when in the background image forming apparatus a color-matching pattern is detected with a sensor, the sensor may erroneously detect a seam mark formed on a seam by regarding the seam mark as the color-matching pattern. Erroneously detecting such a seam mark pattern causes a difficulty in improving a precision of image formation control performed based upon a signal obtained by detecting the color-matching pattern with the sensor.
When an intermediate transfer belt is formed seamless and integral, erroneous detection of the seam mark as a color-matching pattern can be avoided. However, in order to form an intermediate transfer belt to be seamless and integral, complex manufacturing steps are generally needed, and thereby a manufacturing cost increases as a drawback.